The long range goal of the proposed research is to learn how the gamma interferon receptor is involved in the regulation of macrophage activation for tumor cell killing. The rationale for undertaking the proposed research is that murine gamma interferon (MuIFN-gamma), which is one form of macrophage activating factor, mediates its effects through a membrane receptor. Investigation of the receptor should, therefore, yield information that is pertinent to identifying the early events that are involved in the induction of macrophage activation. The availability of large amounts of recombinant murine gamma interferon from Genentech Inc., as well as homogenous populations of cultured macrophages have made these studies feasible. They will include: (1) receptor binding studies, designed to quantify the number and binding affinity of MuIFN-gamma receptors on unstimulated macrophages, as well as those with either increased responsiveness to MuIFN-gamma (inflammatory macrophages) or diminished responsiveness (postcytolytlc macrophages). Computer-assisted analysis (LIGAND program) of Scatchard plots will be the principal approach here; (2) enrichment of the MuIFN-gamma receptor complex from macrophage membranes, either with or without chemical crosslinking; (3) preparation of monoclonal antibodies against the receptor. These monoclonal antibodies will be used to immunopurify the receptor, as well as to determine whether or not antireceptor antibody binding can functionally mimic binding of MuIFN-gamma; and (4) partial physicochemical and biochemical characterization of the isolated MuIFN-gamma receptor. If time allows, additional studies will be performed to preliminarily characterize the receptor with regard to its functional type. With general indications as to the functional type, it should then be possible to design definitive studies that will show how the receptor initiates the events that induce activation. The proposed research is significant because it will yield new, basic information about an important host defense mechanism, macrophage activation for tumor cell killing. It is expected that much of the knowledge obtained will be equally applicable to understanding how MuIFN-gamma modulates a variety of other macrophage characteristics and functions, ranging from induction of an antiviral state to phagocytes or antigen presentation. To our knowledge, these will be the first studies of the gamma interferon receptor on macrophages. (HF)